Issue 5 Evil Winter 2001/02

Raw and Processed Data

In April 2001, the Fund for the City of New York released a report
that quantified the smoothness of the streets of New York.1 The
Fund hired a firm that specializes in measuring the profiles of highways
and airport runways to gather data on approximately 670
miles of the city's streets chosen at random. The New York street
profiles were measured by a car which had a laser scanning device
known as a profilometer attached to its side. The profilometer scans
the ground and gets a reading every 0.011 inches when the car is
driven at 20 mph.

The raw data, accurate to a thousandth of an inch, was then
converted into two standard indices: the International Roughness
Index (IRI) developed by the World Bank in the 1970s to measure
road roughness, and the Bump Index developed by Boeing to evaluate
runways for takeoff and landing. The World Bank provides a
computer program that will process the raw data and generate the
Roughness Index. The IRI indicates the total accumulated deflection
of the suspension of a theoretical car per distance traveled.2
Boeing's Bump Index measures the ratio of the bump height to the
bump length. A Bump Index of above 1.0 on a runway is considered
dangerous for planes taking off or landing.

The Technical Appendix of the Fund’s report tantalizingly mentions
the manual rod-and-level method as an alternative method for
generating the raw data for those who cannot afford the profilometer.
One sunny day in October, when no subscriptions had come in
and all our article ideas looked doomed, we decided to try the manual
technique to measure the three blocks immediately adjacent to
our office. We then processed the data using the IRI and Bump Index.
The results are on the preceding pages. We do not recommend that
you try this. It is laborious and teaches you nothing.

See www.fcny.org/cmgp/streetsmoothness [link defunct—Eds.] for an online copy of the report. The Appendix
has useful technical information.

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